More from WebMD

Aug. 15, 2011 -- Watching six hours or more of TV per day could shorten the average life expectancy by nearly five years, a study suggests.

Researchers say it's the first study to look at the loss of life associated with this sedentary activity.

"TV viewing time may have adverse health consequences that rival those of lack of physical activity, obesity and smoking," write researcher J. Lennert Veerman, of the University of Queensland, Australia, and colleagues in the British Journal of Sports Medicine. "Every single hour of TV viewed may shorten life by as much as 22 minutes."

Previous studies have already linked sedentary behavior with a higher risk of death, especially from heart attack or stroke.

Watching TV is known to account for a large amount of sedentary activity. But researchers say until now its impact on life expectancy has not been measured independently.

TV Watching and Life Expectancy

In the study, researchers used a combination of survey data starting in 1999-2000 until 2008 and death figures for Australia to calculate life expectancies associated with TV watching. The people in the survey answered questions about how much time they had spent in the previous week watching TV or videos.

Based on the results, researchers estimated that Australian adults aged 25 and older watched 9.8 billion hours of TV. Every single hour of television watched after age 25 was associated with a 22-minute reduction in average life expectancy.

Researchers say their calculations show that an adult who spends an average of six hours per day watching TV can expect to live 4.8 years fewer than someone who does not watch TV.

In comparison, previous research has shown that lifelong smoking is associated with a four-year reduction in life expectancy after age 50. The average loss of life from one cigarette is estimated to be 11 minutes, or the equivalent of watching half an hour of TV, according to this study.

Researchers say the study is based on Australian data but the findings should be comparable in other industrialized countries, such as the U.S.